I need help finding the title of this movie I had to have watched sometime between 2009-2016 where the movie takes place in the middle of some kind of zombie apocalypse. The main characters are this brother and what I think is his little sister (?) but nonetheless a young girl who is traveling with him. I can’t remember anything too plot-specific, but there are two key scenes I remember from this film.
In the climax of the movie, their group is running from a horde of zombies and into some chamber which has a gate that will close between the MCs and the horde. In order to save her brother and their friends, the little girl stays back and fights off the zombie horde while the gate closes. Everyone thinks she dies but then the gate opens to find that she killed them all.
At the literal end of the movie when the brother is with his new girlfriend in their room, they are implied to start having sex and the camera pans up to the ceiling/vents where the little girl is watching them.
I also vaguely remember there being a scene where their group goes to an abandoned mall of some sort and they watch the remnants of some sort of news channel explaining that there has been an outbreak of some virus that is causing people to turn into these zombie-like monsters.